This study focused on the estimation of muscle force developed by electrical stimulation to evaluate muscle fatigue during FES control. Muscle force, M-wave, and oxygenated hemoglobin and deoxygenated hemoglobin levels in a muscle were measured simultaneously under isometric conditions during electrical stimulation with three neurologically intact subjects. The oxygen consumption rate was estimated from the measured hemoglobin levels. Electrical current stimulation with 20Hz of frequency and 0.3ms of pulse width was applied to the right vastus lateralis muscle through surface electrodes. Stimulus pulse amplitude patterns were (a) long-term constant stimulation (increase for 10s and maximum for 590s) and (b) repetition of short-term constant stimulation (increase for 10s and maximum for 50s) with 10s interval (intermittent stimulation). The M-wave amplitude and the oxygen consumption rate were approximated to muscle force by the first-order linear equation, using the least-squares method. The results showed that the M-wave would be effective for muscle force estimation before severe muscle fatigue. The M-wave was also found to be useful in predicting muscle force decrease caused by muscle fatigue. As for the oxygen consumption rate, it was suggested that the rate would be useful for muscle force estimation during long-term stimulation, excluding the beginning of the stimulation. The reasons why the M-wave amplitude varied unstably when electrical stimulation was applied continuously more than 200 s and why the oxygen consumption rate was delayed from muscle force at the beginning of the first stimulation must be clarified.
|Number of pages
|Japanese Journal of Medical Electronics and Biological Engineering
|Published - 2002